JP 2007-240496 A published by the Japan Patent Office in 2007 discloses a torque sensor for a steering system of a vehicle. The torque sensor detects a steering torque input into a torsion bar without contact.
The torque sensor comprises a magnetic force generating part which rotates together with a base of the torsion bar that has been operated to rotate, a rotating magnetic circuit which rotates together with an output shaft connected to a tip of the torsion bar, a fixed magnetic circuit fixed to a housing, and a magnetic sensor which detects a magnetic flux density in the fixed magnetic circuit.
As the torsion bar undergoes a torsional deformation due to an input torque, the magnetic force generating part rotates relative to the rotating magnetic circuit, and the magnetic flux density which the rotating magnetic circuit receives from the magnetic force generating part varies.
The rotating magnetic circuit and the fixed magnetic circuit are configured to transmit magnetic flux without contacting. By detecting the density of the magnetic flux in the fixed magnetic circuit using the magnetic sensor, it is possible to detect a torque acting on the torsion bar.
To transmit the magnetic flux from the rotating magnetic circuit to the fixed magnetic circuit, the rotating magnetic circuit comprises a pair of soft magnetic rings. The fixed magnetic circuit comprises a pair of magnetic collecting rings fixed to the inner peripheral surface of the housing.
One of the magnetic collecting rings is disposed to permanently face the outer peripheral part of one of the soft magnetic rings. The other magnetic collecting ring is disposed to permanently face the outer peripheral part of the other soft magnetic ring. According to this arrangement, when the magnetic collecting ring rotates relative to the corresponding soft magnetic ring, the magnetic flux density transmitted from the soft magnetic ring to the magnetic collecting ring does not vary. By providing such a magnetic flux transmission mechanism, the magnetic sensor can detect the torque acting on the torsion bar without contact.